The present invention relates generally to an optically transparent or translucent biocidal composition that releases chlorine dioxide upon being activated, and methods of using the composition.
Chlorine dioxide (ClO.sub.2) is a superior oxidizing agent widely used as a bleach, disinfectant, fumigant or deodorizer. It can penetrate the cell wall or membrane and cytoplasm of mold spores, bacteria and other microbiological contaminants at concentrations below one part per million and destroy them.
Chlorine dioxide or sodium chlorite have also been incorporated in food packaging. Studies have shown that residual levels of such preservatives do not result in a significant genetic or carcinogenic hazard to humans. Meier et al. studied the effect of subchronic and acute oral administration of chlorine, chlorine dioxide, sodium chlorite and sodium chlorate on the induction of chromosomal aberrations and spermhead abnormalities in mice Environ. Mutagenesis, 7, 201 (1985)!. Only the highly reactive hypochlorite resulted in a weak positive effect for mutagenic potential. The other compounds, including chlorine dioxide and sodium chlorite, failed to induce any chromosomal aberrations or increased numbers of micronuclei in the bone marrow of mice. Vilagines et al. attribute the relatively innocuous effect of chlorine dioxide to its inability to produce halomethanes, unlike hypochlorite and chlorine Proc. AWWA Disinfect. Semin., 24 pp. (1977); Chem. Abs. 93, 173513f!. Recently, Richardson et al. reported that an EPA study of the reaction of chlorine dioxide with water borne organics confirmed this observation Environ. Sci. Technol., 28, 592 (1994)!.
Japanese Kokai Nos. 63/296,758, 63/274,434, and 57/168,977 describe deodorants containing chlorine dioxide incorporated in a polymer, ceramic beads, or calcium silicate wrapped in nonwoven cloth, respectively. Gels that generate chlorine dioxide for use as topical applications for disinfection are disclosed by Kenyon et al., Am. J. Vet. Res., 45(5), 1101 (1986). Chlorine dioxide generating gels are generally formed by mixing a gel containing suspended sodium chlorite with a gel containing lactic acid immediately prior to use to avoid premature chlorine dioxide release. Chlorine dioxide releasing gels have also been used in food preservation.
Encapsulation processes have also been used in preparing sources of chlorine dioxide. Canadian Patent No. 959,238 describes generation of chlorine dioxide by separately encapsulating sodium chlorite and lactic acid in polyvinyl alcohol and mixing the capsules with water to produce chlorine dioxide.
Tice et al. U.S. Pat. No. 4,585,482 describes gradual hydrolysis of alternating poly(vinyl methyl ether-maleic anhydride) or poly(lactic-glycolic acid) to generate acid that can release chlorine dioxide from sodium chlorite. A polyalcohol humectant and water are encapsulated with the polyanhydride or polyacid in a nylon coating. After sodium chlorite is diffused into the capsule through the nylon wall, an impermeable polystyrene layer is coacervated around the nylon capsule to retain water within the capsule. The capsules can be coated onto surfaces to release chlorine dioxide. Although the capsules are said to provide biocidal action for several days to months, chlorine dioxide release begins immediately after the capsules are prepared. The batchwise process used to prepare the capsules also involves numerous chemical reactions and physical processes, some of which involve environmental disposal problems.
Wellinghoff et al. have formulated composites that include a hydrophobic phase containing an acid releasing agent and a hydrophilic phase containing chlorite anions. The composite is substantially free of water until it is exposed to moisture. Once exposed to moisture, acid and hydronium ions are generated in the hydrophobic phase. The hydronium ions migrate to the hydrophilic phase and react with chlorite anions to release chlorine dioxide from the composite. These composites are composed of and generate only FDA approved substances or substances generally recognized as safe. The composites can be used for food packaging and other applications where the substances can be ingested by or in contact with humans. These composites are described in U.S. Pat. Nos. 5,360,609, 5,650,466, 5,707,739, 5,631,300, 5,668,185, and 5,705,902.
Wellinghoff et al. U.S. patent application Ser. No. 08/924,684 discloses a composite formulated for maximum chlorine dioxide release in which the hydrophilic material contains an .alpha.-amino ether and a chlorite salt formed by reaction of an iminium chlorite and a base. Iminium chlorite is unstable to nucleophilic attack by the chlorite anion. When the iminium chlorite is reacted with a base, however, the more stable .alpha.-amino ether and chlorite salt are formed.
Wellinghoff et al. U.S. Pat. No. 5,639,295 describes a method for maximizing chlorine dioxide release from an amine-containing composite by omitting the chlorite source until the composite is applied to a surface. After application, the composite is exposed to chlorine dioxide gas that either reacts with the amine to form iminium chlorite in situ or dissolves in the amine to provide chlorite anions. The composite is then activated in the presence of moisture to release chlorine dioxide. The composite can be exposed to elevated temperatures during processing, storage and application because the hydrophilic material does not contain iminium chlorite or any chlorite anions that could decompose at such temperatures. The method also precludes premature release of chlorine dioxide from the composite.
Barenberg et al. U.S. patent application Ser. No. 08/724,907 describes numerous methods of using composites such as those disclosed by Wellinghoff et al. to retard bacterial, fungal, and viral contamination and growth of molds on food, produce, meat, and other materials and to deodorize carpeting and the like.
Although the Wellinghoff et al. composites are effective biocides, there is a need for biocidal compositions in which the acid releasing component and the chlorite containing component form an optically transparent or translucent, single-phase mixture.